Machine for covering wires with insulating materials



Sept. 1946. a. H. WALTON ETVAL 2,497,354

MACHINE FOR COVERING WIRES WITH INSULATING MATERIALS Filed Dec. 24, 1943 '2 Sheets-Sheet 2 CEaRc: H. WALTON,

JOSHUA C. Qua YLE 2 Farm Jams I nventors tlorneys Patented Sept. 10, 1946 MACHINE FOR COVERING WIRES WITH INSULATING MATERIALS George Hall Walton, Helsby, near Warrington, Joshua Creer Quayle, Helsby, and Peter Jones, Kelsail, near Chester, England, assignors to British Insulated Cables Limited, Prescot, England, a British company Application December 24, 1943, Serial No. 515,506 In Great Britain January 1, 1943 8 Claims.

In the covering of wires with insulating material by the so-called longitudinal method, two sheets of unvulcanised rubber in the form of long strips are passed longitudinally between a pair of circumferentially grooved rolls With a group of parallel wires between them. The grooves in the rolls register with each other and form at the nip circular apertures or passes through each of which passes a wire with parts of the two sheets of insulating materiah one forming the upper and the other the lower half of the covering of the wire. At each side of each groove the two sheets of rubber are very forcibly compressed so that they are almost severed and seams are formed at each side of the wire bet com the upper sheet and the lower sheet by the forcible compression of the insulating material there. These machines were developed on the basis of the use of sheets of unvulcanised rubber compound which possess the property of forming a seam under compression at normal atmospheric temperatures.

In the invention set out in the application for Letters Patent No. 472,338 the longitudinal machine is adapted for use with other materials, for instance, plasticised polyvinyl compositions which require to be at a temperature substantially above normal atmospheric temperature in order that satisfactory seams can be made by compression between the rolls.

In that improved machine the heating of the sheets of insulating material is effected by passing each sheet by itself, or with the other sheet, through heating means, as the sheets are approaching the grooved nipping rolis. The preferred means of heating is by the utilisation of the effect of a high frequency alternating or fluctuating field, through which the material passes as it is approaching the rolls and arrangements are mentioned in which electrodes are arranged near the path of the sheets, or each sheet of material, so that as the material moves past these electrodes it is subjected to a, high frequency electric field, either between a pair of electrodes or between the wires and an electrode.

It i also mentioned in the said specification that it may be advantageous to supplement this heating by some localised treatment of the sheets as they approach the nip. The present invention makes an addition to or modificationof the machine described in the said specification by which heating is provided in the immediate neighbourhood of the nip with very simple changes in the apparatus. In accordance with the invention, in a machine in which the two sheets of material are kept apart until they are about to enter the nip, heating by a high frequency electric field is effected by feeding high frequency current to the wires in such a way as to establish a field in the insulating material when it comes close to and in contact with these wires. In doing this advantage is taken of the resonant efiect of an insulated line for the purpose of producing a rise of voltage between the point of feeding the wires and the point at which the high frequency heating has to become efiective. This rise of voltage is, as is well-known, dependent upon the distance between the point of feeding the line and the point of terminating it and on the nature of the termination. The best distance is in the neighbourhood of a quarter of the wave length corresponding to the high frequency voltage applied. Since the termination in this case will have the character of capactitative reactance combined with resistance, the distance between the point of feeding and the point of terminating will be somewhat less than a quarter wave length and can be found readily by experiment.

Since it is contemplated that for this heating a frequency of the order of 20 million cycles per second and upwards will be used, it will be seen that the length in question is not an inconvenient one.

Three embodiments of the invention are indicated in the accompanying diagrammatic drawmgs.

In Figure l, which is a side elevation, an arrangement is indicated such as described in the said specification for heating the two sheets of insulating material by high frequency electric fields as they are approaching the rolls and the present invention is shown as an additional heating means in such a machine. In the other ligures the apparatus for heating the sheets of material as they approach the rolls is not shown, only those parts being indicated which represent the present invention.

Figure 2 is a plan view corresponding to Figure 1.

Figure 3 is a side elevation of another arrangement and Figure 4 is the corresponding plan view.

A third arrangement is shown in Figure 5 in side elevation and in Figure 6 this is shown in plan view.

The sheets of insulating material i and 2, as shown in Figure 1, approach the grooved rolls 3 by paths which lead each of them between the two electrodes of a high frequency electric field system. These consist of a lower electrode formed of a metal band 4, passing round a pair of rollers 5, andan upper electrode which is a stationary plate 6. The moving band 4 facilitates the travel of the sheet of material which rests on it and which moves without touching the stationary electrode 6. The moving band is at ground potential and the stationary electrode receives the high potential. From the left-hand ends of the bands 4 the two sheets of material move respectively downward and upward and come together at the nip of the rolls 3, resting against these rolls during the last part of the movement. In the space between the two sets of electrodes 4 and 6 run horizontally a set of parallel wires i which are aligned with the grooves in the rolls 3 so that each wire when passing through the nip of the rolls lies within a groove and is enclosed between portions of the two sheets of insulating material I and 2. This material, which may, for instance, be a plasticised polyvinyl compound, requires to be heated sufficiently to become soft and adhesive so that by the compression of the parts of the rolls between the grooves the material is made to fiOW laterally into the grooves and is caused to make a seam at each side so that it proceeds beyond the rolis as a tube 8 enclosing a wire, the several tubes being connected only by very thin webs of material so that the covered wires can be easily separated from each other.

To ensure that the two sheets of material shall be at the right temperature at the moment of coming into contact in the nip of the rolls 3,

heating localised in that region is provided in accordance with the present invention by setting up a strong high frequency electric field between the wires l and the rolls 3. This field passes through the sheets of insulating material I and 2 and generates heat therein by dielectric loss, the heating being most intense in the direct neighborhood of each wire.

The present invention provides for obtaining the necessary high voltage between wires '1 and rolls 3 in a most convenient manner. It takes advantage of the well-known fact that a conductor in a resonant line having a length ap proximately equal to one-quarter wave length corresponding to the frequency of a high frequency electric supply system will have on it a standing wave of electric potential and another inversely disposed standin wave of electric current so that it can be fed at th low potential end with a substantial current and will exhibit at the other end a high potential difference and a small or zero current. The wires 1 of the present case are made to serve as such a line, the feeding end being that remote from the rolls so that the high potential end is at the rolls. Three systems by which this is carried out are shown in the drawings. In each of them the dimension which approximates to one-quarter wave length is indicated by L. The feeding end is near the right-hand end of this length in each case so that the high. potential end is at the left-hand where the rolls are situated.

In the arrangements shown in Figures 1 and 2 two sides of a line are provided by two groups of wires which are spaced apart laterally. The nodal point, i. e., the voltage minimum point, is located by the grounded short-circuiting bar 9 across and in contact with which all the wires 1 run. Near the rolls 3 the wires are supported on an insulating bar iii. This is provided solely for the. purpose of raising the level of the wires slightly. for convenience in the disposition of the apparatus. The arrangement described provides a quarter-wave length line short circuited at the voltage nodal point and connected through two small capacities in series at the rolls, each of these capacities being formed by a group of wires l, the dielectric consisting of the sheets of material i and 2 and the second electrode provided by the rolls 3. Into this line is fed high frequency current by means of the coupling loop ll placed near the voltage nodal point 9 and connected with the oscillator [9.

The arrangement shown in Figures 3 and 4 is similar in principle to that just described, but provides a better utilisation of the width of the rolls 3 since it is unnecessary here to provide a clear space between the two sets of wires 1 at the rolls At this end of the line the wires approach together as shown clearly in. Figure 4. They are separated into two sets by guides l2 and it. Each of the guides i2 is a block of insulating material, standing vertically, with holes for the wires arranged in a vertical line. The uide members l3 are vertical bars of conducting material which are both grounded and thereby conn ected together and form, not only a guide, but a short-circuiting connection at the nodal point. By this arrangement of guides and by appropriate means for leading the wires from the supply bobbins to the guides I3, the wires are divided into two vertical sets until they reach the guides i2 from which point they begin to turn into a single horizontal plane which they reach at the nip of the rolls 3. The feeding in this case is also done by means of a loop ll receiving high frequency current from an oscillator (not shown).

In the arrangement shown in Figures 5 and 6', the wires i are used in a single set as one side of the line, the other side being provided by a strip M of metal arranged below the wires 1 and connected at the right-hand end to the short circuiting bar l5 which is grounded and locates the nodal point. At the left-hand end the strip It makes contact with one of the rolls 3 by means of brushes It. The two rolls are connected together electrically by their housing. In this case the housing and the rolls are insulated from ground, as indicated diagrammatically by the insulated platform I! shown in Figure 5. The feed to the line could in this also be by way of a loop placed between the wires 1 and the strip [4, but an alternative arrangement is shown in which the feed is by a conductive connection from the oscillator l9 by way of the short circuiting bar 15 and another bar I8 placed a short distanc away from it and insulated from ground.

The arrangement shown in Figures 5 and 6 has a combination of advanta es of simplicity, convenience and efficiency. but other dispositions of the parts of the machine are possible using the wires in one set as one side of the line.

The arrangement shown in Figures 5 and 6 also has the advantage that the high frequency fields are mainly located in the space between the wires and the strip l4 so that losses in the surrounding bodies are small.

It will be seen that the additional heating means provided by the present invention can very conveniently be applied to the wires as they are led into the machine and thereby heat can be generated in the insulating material at the point where the highest temperature of this material is required and this is done in a way which. facilitates the disposition of the high voltage part of the apparatus.

What we claim as our invention is:

1. Apparatus for heating pairs of strips of organic resin insulation by dielectric loss as they enter the nip of a pair of cooperating electrically conducting rolls having a plurality of opposed grooves therein, each pair of grooves defining a pass for continuously applying said strips as a coating to an electrically conducting wire travelling through said pass and seaming together the strips applied to each wire, said apparatus comprising a capacitor formed by the insulation strips together with the rolls and the portions of the wires in the nip thereof, a resonant transmission line having two parallel sides so connect ed to said capacitor as to apply high-frequency voltage thereto, at least one side of said line consisting of a length of at least one of said wires on the entering side of said rolls and conductive- 1y related to the portion of said one of said wires in the/nip of the rolls, means electrically connecting the two sides of the line together at a point in said length distant from said rolls by nearly one quarter of the Wave-length corresponding to said frequency, and means between said point and the rolls for feeding said highfrequency electric energy into said line.

2. The apparatus defined by claim 1 having the two sides of the said line constituted by two spacially separated groups of the said wires.

3. The apparatus defined by claim 1 having the two sides of the said line constituted by two spacially separated groups of the said wires all lying in one and the same plane.

4. The apparatus defined by claim 1 having the two sides of the said line constituted by two spacially separated groups of the said Wires, the

wires of one group lying in one plane and the wires of the other group lying in another plane parallel therewith, and means located near to the rolls for bringing all the wires into one plane.

5. The apparatus defined by claim 1 having one side of the said line constituted by all of the said wires in parallel and the other side by an electrically conductive member extending alongside said wires between the said connecting means and the rolls, and means for coupling said memher at one end thereof to the said connecting means and at the other end thereof to the rolls.

6. The apparatus defined by claim 1 having the said feeding means coupled to the line in the part thereof directly adjacent to the said point whereby to obtain a large rise in voltage between said feeding means and the two sides of the line at the rolls.

7. The apparatus defined by claim 1 having said feeding means constituted by a coupling loop adjacent the line and the said point and an oscillator electrically connected to said loop.

8. The apparatus defined by claim 1 having said. feeding means constituted by an oscillator, an electrically conductive connection from said oscillator to the line at said point and another electrically conductive connection from said osoillator to a point in one side of said line located a distance from said point which is only a minor roportion of the length from said point to the rolls.

GEORGE HALL WALTON. JOSHUA CREER QUAYLE. PETER JONES. 

